1. Field of the Invention
This invention relates generally to a method for the control of oil and gas production wells. More particularly, it relates to a communication protocol for a multi-well, multi-zone control system for providing communications signals between components of the system to ensure that each component reliably receives communications intended for it.
2. Description of the Related Art
The control of oil and gas production wells constitutes an on-going concern of the petroleum industry due, in part, to the enormous monetary expense involved as well as the risks associated with environmental and safety issues.
Production well control has become particularly important and more complex in view of the industry wide recognition that wells having multiple branches (i.e., multilateral wells) will be increasingly important and commonplace. Such multilateral wells include discrete production zones which produce fluid in either common or discrete production tubing. In either case, there is a need for controlling zone production, isolating specific zones and otherwise monitoring each zone in a particular well. Before describing the current state-of-the-art relative to such production well control systems and methods, a brief description will be made of the production systems, per se, in need of control. One type of production system utilizes electrical submersible pumps (ESP) for pumping fluids from downhole. In addition, there are two other general types of productions systems for oil and gas wells, namely plunger lift and gas lift. Plunger lift production systems include the use of a small cylindrical plunger which travels through tubing extending from a location adjacent the producing formation down in the borehole to surface equipment located at the open end of the borehole. In general, fluids which collect in the borehole and inhibit the flow of fluids out of the formation and into the wellbore, are collected in the tubing. Periodically, the end of the tubing is opened at the surface and the accumulated reservoir pressure is sufficient to force the plunger up the tubing. The plunger carries with it to the surface a load of accumulated fluids which are ejected out the top of the well thereby allowing gas to flow more freely from the formation into the wellbore and be delivered to a distribution system at the surface. After the flow of gas has again become restricted due to the further accumulation of fluids downhole, a valve in the tubing at the surface of the well is closed so that the plunger then falls back down the tubing and is ready to lift another load of fluids to the surface upon the reopening of the valve.
A gas lift production system includes a valve system for controlling the injection of pressurized gas from a source external to the well, such as another gas well or a compressor, into the borehole. The increased pressure from the injected gas forces accumulated formation fluids up a central tubing extending along the borehole to remove the fluids and restore the free flow of gas and/or oil from the formation into the well. In wells where liquid fall back is a problem during gas lift, plunger lift may be combined with gas lift to improve efficiency.
In both plunger lift and gas lift production systems, there is a requirement for the periodic operation of a motor valve at the surface of the wellhead to control either the flow of fluids from the well or the flow of injection gas into the well to assist in the production of gas and liquids from the well. These motor valves are conventionally controlled by timing mechanisms and are programmed in accordance with principles of reservoir engineering which determine the length of time that a well should be either xe2x80x9cshut inxe2x80x9d and restricted from the flowing of gas or liquids to the surface and the time the well should be xe2x80x9copenedxe2x80x9d to freely produce. Generally, the criteria used for operation of the motor valve is strictly one of the elapse of a preselected time period. In most cases, measured well parameters, such as pressure, temperature, etc. are used only to override the timing cycle in special conditions.
It will be appreciated that relatively simple, timed intermittent operation of motor valves and the like is often not adequate to control either outflow from the well or gas injection to the well so as to optimize well production. As a consequence, sophisticated computerized controllers have been positioned at the surface of production wells for control of downhole devices such as the motor valves.
In addition, such computerized controllers have been used to control other downhole devices such as hydro-mechanical safety valves. These typically microprocessor based controllers are also used for zone control within a well and, for example, can be used to actuate sliding sleeves or packers by the transmission of a surface command to downhole microprocessor controllers and/or electromechanical control devices.
The surface controllers are often hardwired to downhole sensors which transmit information to the surface such as pressure, temperature and flow. This data is then processed at the surface by the computerized control system. Electrically submersible pumps use pressure and temperature readings received at the surface from downhole sensors to change the speed of the pump in the borehole. As an alternative to downhole sensors, wire line production logging tools are also used to provide downhole data on pressure, temperature, flow, gamma ray and pulse neutron using a wire line surface unit. This data is then used for control of the production well.
A problem associated with known control systems is the reliability of surface to downhole signal integrity. It will be appreciated that should the surface control signal be in any way compromised on its way downhole, then important control operations will not take place as needed. As distances between the surface system and downhole controllers increases, the signal is attenuated and may fall below a level required for reliable communication.
The methods and apparatus of the present invention overcome the foregoing disadvantages of the prior art by providing a reliable method of communication for a multi-well, multizone completion system.
In one aspect, a method for controlling production from a formation having at least one producing well disposed therein, the at least one producing well having a plurality of producing zones, comprises; installing a flow control device with a controller proximate each of the producing zones where each controller has a predetermined communication address, and each controller is adapted to act as a repeater on command from a surface controller; connecting each controller to a transmission bus, where the transmission bus is connected to the surface controller; transmitting a command message from the surface controller to a predetermined controller, where the command message determines a predetermined path along the transmission bus according to a predetermined protocol; receiving the command message by the predetermined controller; and executing the command message to control the flow control device.
In another aspect of the present invention, a method involves transmission of a command message from a master node, through at least one repeater node, to a destination node, each node having a separate unique address to ensure that the message is repeated, received, and executed only by the intended nodes. The method comprises transmitting a command message on a communication bus from a master node, having the message relayed by at least one repeater node to a destination node. The command message comprises a command synchronization string, a command origin address, at least one repeater address, and a destination address. The path of the message is determined by routing information in the address of each node in the header. The destination node interprets and executes the message and sends a response message by modifying the routing bits to retrace the path of the command message. The response message is received and interpreted by the master node and used by the surface system to control the well production.
In another preferred embodiment, the method involves transmission of a command message from a master node to a destination node, each node having a separate unique address to ensure that the message is received, and executed only by the intended node. The method comprises transmitting a command message on a communication bus from a master node to a destination node. The command message comprises a command synchronization string, a command origin address and a destination address. The path of the message is determined by routing information in the address of each node in the header. The destination node interprets and executes the message and sends a response message by modifying the routing bits to retrace the path of the command message. The response message is received and interpreted by the master node and used by the surface system to control the well production.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.